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https://issues.apache.org/jira/browse/HDFS-16689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17584511#comment-17584511
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ASF GitHub Bot commented on HDFS-16689:
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xkrogen commented on PR #4744:
URL: https://github.com/apache/hadoop/pull/4744#issuecomment-1226624906
> I'm sorry, I just find this comment, but didn't find related code to
finalize the previous inProgress segment. Can you share the related code?
Thanks.
I'm referring to this:
https://github.com/apache/hadoop/blob/62c86eaa0e539a4307ca794e0fcd502a77ebceb8/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/Journal.java#L574-L583
But a little more digging made me realize that I don't think what I
described will actually happen, since in `FSEditLog#openForWrite()` before
calling `startLogSegment()` we first check that there are no active streams:
https://github.com/apache/hadoop/blob/63db1a85e376c2266afdc62b9590e40acc98429c/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSEditLog.java#L338-L347
So it will actually throw an exception, rather than finalizing the old
segment as I said previously. But this is _after_ `catchupDuringFailver()`, so
to make your original proposal (disable in-progress edits) work properly, we
still need to modify `recoverUnclosedStreams()` to throw an error when it fails
instead of just swallowing the exception.
I briefly looked at the other usages of `recoverUnclosedStreams()` and I
don't really see any reason why we would want to swallow the exception ... The
TODO comment there is also from 2012, 10 years old now :)
So are we agreed that the best way forward is to modify
`recoverUnclosedStreams()` to throw exception on failure, then we can use
`inProgressOk = false` to solve this problem as you originally proposed?
> Standby NameNode crashes when transitioning to Active with in-progress tailer
> -----------------------------------------------------------------------------
>
> Key: HDFS-16689
> URL: https://issues.apache.org/jira/browse/HDFS-16689
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: ZanderXu
> Assignee: ZanderXu
> Priority: Critical
> Labels: pull-request-available
> Fix For: 3.4.0
>
> Time Spent: 50m
> Remaining Estimate: 0h
>
> Standby NameNode crashes when transitioning to Active with a in-progress
> tailer. And the error message like blew:
> {code:java}
> Caused by: java.lang.IllegalStateException: Cannot start writing at txid X
> when there is a stream available for read: ByteStringEditLog[X, Y],
> ByteStringEditLog[X, 0]
> at
> org.apache.hadoop.hdfs.server.namenode.FSEditLog.openForWrite(FSEditLog.java:344)
> at
> org.apache.hadoop.hdfs.server.namenode.FSEditLogAsync.openForWrite(FSEditLogAsync.java:113)
> at
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startActiveServices(FSNamesystem.java:1423)
> at
> org.apache.hadoop.hdfs.server.namenode.NameNode$NameNodeHAContext.startActiveServices(NameNode.java:2132)
> ... 36 more
> {code}
> After tracing and found there is a critical bug in
> *EditlogTailer#catchupDuringFailover()* when
> *DFS_HA_TAILEDITS_INPROGRESS_KEY* is true. Because *catchupDuringFailover()*
> try to replay all missed edits from JournalNodes with *onlyDurableTxns=true*.
> It may cannot replay any edits when they are some abnormal JournalNodes.
> Reproduce method, suppose:
> - There are 2 namenode, namely NN0 and NN1, and the status of echo namenode
> is Active, Standby respectively. And there are 3 JournalNodes, namely JN0,
> JN1 and JN2.
> - NN0 try to sync 3 edits to JNs with started txid 3, but only successfully
> synced them to JN1 and JN3. And JN0 is abnormal, such as GC, bad network or
> restarted.
> - NN1's lastAppliedTxId is 2, and at the moment, we are trying failover
> active from NN0 to NN1.
> - NN1 only got two responses from JN0 and JN1 when it try to selecting
> inputStreams with *fromTxnId=3* and *onlyDurableTxns=true*, and the count
> txid of response is 0, 3 respectively. JN2 is abnormal, such as GC, bad
> network or restarted.
> - NN1 will cannot replay any Edits with *fromTxnId=3* from JournalNodes
> because the *maxAllowedTxns* is 0.
> So I think Standby NameNode should *catchupDuringFailover()* with
> *onlyDurableTxns=false* , so that it can replay all missed edits from
> JournalNode.
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